I get exactly the same issue with my RPI and BV4205. I have looked at the Clk and Data lines with a multimeter and after running i2cdetect the BV4205 jams them in the low state. Hence you can't see any other devices on subsequent runs of i2cdetect after running i2cdetect the first time. Cycling the power to the BV4205 chip then releases the bus. Using an oscillosope on the lines shows actby iand - Serial & I2C Devices